Apparatus and method fob receiving



Feb. 1, 1938. G. c. SOUTHWORTH ET AL 2,105,770

APPARATUS AND METHOD FOR RECEIVING ELECTROMAGNETIC WAVE SIGNALS ON DIELECTRIC GUIDES Filed Oct. 12, 1955 2 Sheets-Sheet 1 C LE "III, "III IIIUIIII ulllwll 707 707 INVENTORS ATTORNE 1938. e. c. SOUTHWORTH ET AL 2,106,770

APPARATUS AND METHOD FOR RECEIVING ELECTROMAGNETIC WAVE SIGNALS ON DIELECTRIC. GUIDES Filed Oct. 12, 19:55 2 Sheets-Sheet 2 Output @Eiig E53 1 EiIL p|l-| INVENTORS 6: C. Somfkzqazrhfl? BY ATTORNE Patented Feb. 1, 1938 PATENT OFFICE APPARATUS AND METHOD FOR RECEIVING ELECTROMAGNETIC WAVE SIGNALS ON DIELECTRIC GUIDES George C. Southworth and Archie P. KIng Red Bank, N. J

'gnors to Bell Telephone Laboratorie s, Incorporated, New York, N. Y., a corporation of New York Application October 12, 1935, Serial No. 44,641

15 Claims.

A principal object of our invention is to provide new and improved apparatus and a corresponding method for the efiective reception of electromagnetic wave signals, especially as they may be transmitted to the place of their reception over adielectric guide. Another object of our invention is to provide for receiving such signals under such circumstances by means of gas or vacuum tubes advantageously combined with the receiving end of a dielectric guide. An-

other object of our invention is to place the input conductors for such tubes so that they will lie along the lines of force of the received waves, whereby the energy of such waves will be applied effectively for the reception of the signals transmitted on them. All these objects and other objects and advantages of our invention will become apparent on consideration of a limited number of specific embodiments of the invention, which we have chosen for disclosure in the following specification. It will be understood that this disclosure relates principally to these particular examples of practice according to the invention and that the scope of the invention will be indicated in the appended claims.

Referring to the drawings, Figures 1, 3, 5, and

'7 are diagrammatic longitudinal sections of a dielectric guide showing the lines of force of respectively different wave typestherein; Figs. 2, 4, 6

and 8 are respective corresponding cross-sections;

Fig. 9 is a diagrammatic cross-section of a dielectric guide at its receiving end showing a cold cathode gas tube as the receiving element together with its associated circuit; Figs. 9a and 9b 3., are modifications of Fig. 9; Fig. 10 is a diagram showing both sending and receiving ends of a dielectric guide with a cold cathode gas tube practically filling the guide at the transmitting end for modulation and another such tube at the reshowing an inductive device for energizing the tubes of Fig. 10, thus dispensing with the plate electrodes of Fig. 10; Fig. 12 shows a tube such as the sending tube of Fig. 10 in' a constricted part of the dielectric guide; Fig. 13 shows a hot cathode gas tube as the detecting element within a dielectric guide at its receiving end; Fig. 14

shows a high vacuum hot cathode two-electrode tube as the receiving element in a dielectric guide;

Fig. 15 shows a hot cathode two-electrode tube in a system adapted for receiving waves of symmetric type; Fig. 16 shows a three-electrode vacuum tube adapted for receiving asymmetric magnetic waves; Fig. 1'7 shows suchatubeforsymmetric magnetic waves; Fig. 18 shows a multiple ceiving end for detection; Fig. 11 is a diagram grid tube for receiving symmetric electric waves; Fig. 19 shows a three-electrode tube which may be adjusted for different uses; Fig. 20 shows a suitable circuit system for a regenerative receiver; Fig. 21 shows proper associated circuits for a Barkhausen oscillator connected to function as an oscillating detector in a wave guide; Fig. 22 shows similar connections for a magnetron oscillator; Fig. 23 shows a three-electrode vacuum tube oscillator with alternative connections so that it maybe used either for receiving or transmitting; and Fig. 24 shows an impedance matching termination for a dielectric guide which incorporates one of the receiving elements disclosed in earlier figures of the drawings,

For the purpose of transmitting electromagnetic waves from one place to another place, a dielectric guide may be provided consisting of a body of dielectric extending from the one place to the other place and bounded laterally by a dielectric discontinuity. A dielectric guide may take various forms, for example, a cylindrical body of air or empty space bounded by a metallic sheath. In Figs. 1 to 8, cylindrical sheaths are shown in longitudinal and transverse section with the sheath wall thickness greatly exaggerated to facilitate the diagrammatic representation.

Certain types of waves in such a dielectric guide may be named and symbolized as follows: They are symmetric if they have symmetry on all sides around the axis, but they are asymmetric if the lines of force lie in great part parallel with a single plane containing the axis. Also, the waves are electric if they have a substantial component of electric force in the direction of propagation, but they are magnetic if they have a substantial component of magnetic force in that direction. In Figs. 1 to 8, continuous lines represent lines of electric force and dotted lines represent lines of magnetic force. Accordingly, symmetric electric waves (E0) are represented in Figs. 1 and 2, symmetric magnetic waves (H0) in Figs. 3 and 4, asymmetric electric waves (E1) in Figs. 5 and 6, and asymmetric magnetic waves (H1) in Figs. 7 and 8.

Assuming that waves of one of the types shown in Figs. 1 to 8 are to be transmitted over a dielectric guide, the present disclosure has to do more particularly with obtaining optimum response from such waves for a given incident signal at the receiving end. It will be obvious in many cases that the configuration and relation of parts at the receiving end will be similarly advantageous at the transmitting end upon the substitution of wave generators for wave energy receivers.

In the disclosures that follow, a suitable wave frequency that may be held in view by way of example will be of the order of 2,000 megacycles per second corresponding to a wave length in free space of about 15 centimeters. For'such a wave length the diameter of the wave guide when it has an air core may advantageously be about 5 inches. The devices described herein are applicable by suitable scale modifications to higher and lower frequencies than that mentioned. In practically all of the arrangements herein disclosed the receiver or detector elements are connected in circuits with the coupling leads lying along the lines of force of the electric field of the received waves. In most of the receivers disclosed herein the received electric wave energy is applied directly in this way, instead of being applied to develop electromotive forces in conductive circuits and thereby convey the electromotive forces along the conductors to the detector or receiver elements at a greater or less distance.

Referring to Fig. 9, this shows a cross-section of a metal-sheathed, air core dielectric guide at its receiving end, adapted for asymmetric magnetic waves. The diametral conductor I has a cold-cathode, two-electrode, gas tube IOI interposed at the center. The plate 06 is in capacity relation to the guide wall, thus affording a connection for the high frequency currents but not for the lower frequency signal currents. The associated circuit of the tube IOI is such thatthe batteries apply a considerable direct electromotive force across the tube IOI, thus maintaining it in a condition of ionization. The indicator at I02 is unaffected by this direct ionization current, being in the bridge member of a Wheatstone bridge, but the device IN is non-linear and any variation of the electromotive forces across its terminals caused by incoming waves will give an indication on I02.

In the modification of Fig. 9 that is illustrated in Fig. 9a, the high frequency pick-up conductors connected to the terminals of the axially-positioned discharge device extend along the diameter but only part way across the guide. Parallel to the diametral plane orthagonal to the one containing the pick-up conductors are brought out from the terminals of the discharge device and through openings in the sheath a pair of con ductors comprising the low, frequencysignaling circuit. The modification illustrated in Fig. 9b is similar to that shown in Fig. 941, but the discharge device is not coaxial with the g'uideand the pick-up conductors are arcuate. This modification bears. obvious relation to the combination described with reference to Fig. 17.

There are other non-linear or asymmetric elements that may be introduced instead of the twoelectrode cold cathode gas tube IOI of Fig. 9 for example. other types of tubes, as will be mentioned in the disclosures that follow.

Gases may be non-linear by virtue of their conductivity or their dielectric constant, or both. The practice has been known to utilize the former property for demonstrating the presence of electric waves in space. Fig. 10 shows how this property may be utilized both at the transmitting and receiving ends in connection with the operation of a dielectric guide. The high-frequency alternating current generator I03 is connected to diametrically opposite points at-the proper distance from the closed end I04 of the metal-' sheathed air core guide I05, so that there will mined experimentally;

be phase reenforcement of the direct and reflected waves at the generator. Accordingly, waves of asymmetric magnetic type are generated and propagated to the right along the guide I05.

Signal modulations are impressed by means of the ionized gas tube I06 which is made to fill practically the entire cross-section of the pipe guide. A state of ionization is maintained by the battery I01 connected with the plates I08 within the tube I06. A television or voice signal or other signal isimpressed through the circuit which is shown in inductive relation with the circuit of the battery I01 and the plates I 00. Corresponding to the variations of current in the signal input circuit, the condition of the gas in the tube I08 is varied and the waves progressing to the right from the generator I03 are modulated accordingly. Ordinarily there will be propagated along the pipe guide I05 the carrier current of the normal frequency of the generator I03 and two side bands representing the modulation effects due to the comparatively low frequency signal currents, which in themselves will not be transmitted along the guide.

At the receiving end of the guide a similarly constructed gas vessel I 06' has circuits very similar to mitting end, the battery I01 in the tube I06 in a state of ionization. The high frequency demodulation currents, representing the signal intelligence, such as voice signals or television signals, are taken off through the inductively related circuit shown in the drawings. Due to the non-linear properties of the gas in the tube I06 there will be produced in the output circuit a demodulation product signal corresponding to the signal impressed at the trans-. mitter.

The tubes I06 and I06 should preferably fill the cross-section of the guide I05 and each should have a length two or three times the length of the waves that are transmitted in the guide. The optimum degree of ionization may be deterit should be of the order of I0 ions per cubic centimeter.

The parallel plates I08 in Fig. may present a discontinuity to the transmitted waves from the generator I03. To obviate this effect, it may be desirable to remove these plates entirely, which can be done in accordance with the modification indicated in Fig. 11. Here both the ionizing field current and the signal current are superposed in the conductive circuit I09 and impressed inductively from the surrounding coil IIO upon the body of gas within the vessel I06. The portion of the dielectric guide sheath I05 which lies within the coil I I0 and around the tube I06 is made metallically discontinuous, but with overlapping edges as indicated at III. Accordingly, the comparatively low frequency currents in the circuit I 09 will not induce substantial currents in the shell I05. At the receiving end the apparatus may be made the same as in Fig. 11, except that the element designated in Fig. 11 as Source of television signals will be an indicator of television signals.

In the operation of the system of Fig. 10 as modified in accordance with Fig. 11 there will be impressed on the modulator a carrier current of about 5 megacycles together with a band of television or other intelligence bearing signals extending from, say, 1 megacycle to 3megacyeles. After suitable amplification the carrier and the two side bands are impressed as an electromagnetic field on the body of gas within the tube I06- is interposed. This those at the transmaintaining the gas The 5 megacycle carrier is of such intensity as to 'maintain the desired degree of ionization when no signal is impressed. The superimposed signal further varies the degree of ionization and thereby produces on the passing waves from generator I03 side bands corresponding not only to the 5 megacycle carrier, but also a plurality of television bands. If the filter shown in Fig. 11 is interposed between the modulator and the amplifier, it removes the carrier and undesired side bands. The side band or side bands passed are effective in the coil IIO upon the body of gas in the tube I06.

By a proper choice of pressure and degree of ionization, the gas in the tube I06 may be made highly absorptive of wave energy. As already mentioned, this makes it possible to use a rather extended vessel of gas at the receiving end of the wave guide so as to act simultaneously as a demodulator and a non-reflecting termination. When the conditions are not favorable for this type of termination, more effective operation may be had by combining the gaseous modulator or demodulator with reactive elements as shown in Fig. 24 which will be discussed farther along in I this specification.

Referring to Fig. 12, the oscillator I03 corresponds to the like designated oscillator of Fig. 10, but here the guide is tapered down to a smaller diameter and its smaller part is occupied by the gas tube H2. The circuit connections are the same as in Fig. 10, but the principle of operation is somewhat different. The degree of ionization within the tube H2 is made to fluctuate in accordance with the signal. For a dielectric guide of given dieletric constant and given diameter there is a critical frequency such that waves of higher frequency are passed but waves of lower frequency are blocked. The diameter at the con-. stricted portion in Fig. 12 is such that waves of the frequency of the generator I03 are blocked at low ionization within the tube II2'. But increasing the ionization within the tube I I2 changes the effective dielectric constant of the gas within that tube, and with the changed dielectric constant the waves that were formerly blocked may now get through. The device is in effect a switch by which the passage of waves from the oscillator I03 is readily controlled. By suitable design, especially by relating the diameter of the constricted part tothe frequency of the generator I03 so that operation is near the cut-off frequency, we may readily produce amplitude modulation of the passing waves.

From what has been said in connection with earlier figures, it will be obvious that with reference to Fig. 12 for the sending end, there may be a corresponding process of demodulation at the receiving end.

Fig. 13 may be compared with Fig. 9, both being adapted for asymmetric magnetic waves. Fig. 13 shows a hot cathode gas tube instead of a cold cathode gas tube. The associated circuit system is similar and the principle of operation is similar. A lower ionization potential is required in Fig. 13 than in Fig. 9, and the impedance will be somewhat lower in Fig. 13 than in Fig. 9.

Whereas Fig. 13 shows a hot cathode gas tube, Fig. 14 shows a hot cathode high vacuum tube. The circuits of Fig. 14 are generally similar to those for Figs. '9 and 13. In both cases, asymmetric magnetic waves may be received. The external resistance R of Fig. 14 may be introduced to make the characteristic of the device more nearly linear. The two-electrode tube of Fig. 14

may be adjusted along the diameter to the optimum position, by making the construction as shown in Figs, 16 and 19. In a particular case of Fig. 14 which worked successfully, the characteristic volt-ampere relation for the tube was substantially in accordance with the equation I=6e where V is the root mean-square value of the impressed voltage, I is the corresponding current through the tube, and e is the base of the Napierian logarithmic system, this equation holding over a considerable range of frequencies.

Fig. v15 shows a multiple anode tube with radial leads adapted for the reception of symmetric electric waves. The common cathode may be indirectly heated.

Three-electrode vacuum tubes may be employed as detectors in accordance with the prin-- ciples of our invention. Fig. 16 shows such a tube in a combination adapted for asymmetric magnetic waves. Here the cathode and grid lead wires lie along a diameter parallel to the lines of electric force of the received waves. All the tube conductors are disposed so that the tube can be adjusted along the diameter, by making the grid and cathode leads in the form of hollow conductors and carrying the plate lead through the grid lead and the cathode heating lead through the cathode lead. The tubular cathode conductor has sliding conductive connection with the guide shell on one side, and on the opposite side,

the tubular grid conductor has sliding conduc- 17. Here the grid lead lies along one of the circles of the lines of electric force, and the corresponding force is applied directly therefrom to the grid.

For the detection or measurement of symmetric electric waves, one may use the specially constructed tube of Fig. 18. The cathode H5 is indirectly heated by the circuit 6-! H, which comprises high frequency choke coils in its radial conductors. The grid is in parts, each part connected to the wave guide wall by a radial conductor such as 8. The conductors H8 and the grid-leads H6 and H1 and the anode lead I20 pass through holes in the enveloping anode H9. Thesignal indicating circuit is taken off across the anode lead I20 and one of the cathode leads H6.

Fig. 19 shows a negative grid three-electrode vacuum tube which may be used at one adjustment as a beating oscillator for beat receiving in connection with asymmetric magnetic waves. At another adjustment it may be used as a regenerative or superregenerative receiver. It may be displaced along the diameter to the position of best operation.

Fig. 20 shows another superregenerative receiver system. The quenching frequency is introduced into the grid circuit by means of the transformer T1. The low frequency component is taken out from the plate circuit by means of the transformer T2.

The use-of a Barkhausen oscillator as an oscillating detector in a wave guide is shown by Fig. 21. This also discloses a quick change switch, permitting the apparatus to be used either as a transmitter or a receiver. As in the negative grid oscillator, the quenching frequency is introduced into the grid circuit, and the low frequency output is obtained from the plate cirup suitably oriented in the field. For

cuit.

- In a similar manner the magnetron oscillator may serve either as a transmitter or as a superregenerative receiver. Both the quenching frequency and the audio output are in the anode circuit as shown in Fig. 22.

The receivers of Figs. 20, 21, and 22 are adapted for asymmetric magnetic waves. The principles bined equipment an alternative transmitter and receiver. A suitable switch changes the detector from a regenerative state to an oscillatory state,

,and at the same time a modulation circuit is I connected to either the grid or plate circuit as desired.

The superregenerative receiver is almost ideally suited for combination transmitter-receiver use. In reception, the detector is prevented from oscillating vigorously by the action of the quenching frequency so that the removal of the latter converts the detector into an oscillator. Since voice frequency modulation may be introduced into the same circuit as the quenching frequency,

a simple switch may be used to connect the grid (or plate) circuit either to the modulation circuit for transmitting or to the quenching frequency circuit for receiving. See, for example, Figs. 21 and 22. Fig. 23 shows the use of a triode as a negative grid oscillator either in a superregenerative receiver orin an oscillator for transmission.

Fig. 24 shows a receiving end system for the effective development and localization oi standing waves in relation to the detector at the receiving end of a dielectric guide. The pistons P1 and P2 are adjusted so that the distance a:

between them is a half wave length or an integral multiple of a half wave length. By shifting the pistons alike, the intermediate standing wave is displaced until its amplitude is such at the place B of connection to the incoming wave guide that there is an impedance match and no reflection of wave energy back into the guide. The detector I35 is then shifted to a place such that there is a match between its impedance and the wave intensity at that place. But the reaction of, the detector may be enough to require a little further readjustment of the pistons P1 and P2 to get an impedance match.

We claim:

1. In combination, a dielectric guide, an electron discharge tube within the guide, a pair of conductors projecting oppositely along the direction of the lines of force of received waves in the guide, and a signal indicating circuit comprising said tube.

2. In combination, a metal-sheathed dielectric guide, an electron discharge tube within the guide, a pair of conductors projecting oppositely therefrom along the direction of the lines of force of received waves in the guide, and a signal indicating circuit comprising said tube, at least therefrom one side of said circuit passing through a small hole in the sheath of said guide without conducsaid pair having no conductive connection with a the sheath where it passes through it.

5. In combination, a metal-sheathed dielectric guide, an electron discharge tube therein; and a signal. indicating circuit comprising said tube and a pair of conductors extending therefrom through said sheath, at least one side of said pair having no conductive connection with the sheath where it passes through it, but having a substantial high frequency capacity relation therewith.

8. In combination, a dielectric guide, for symmetric magnetic waves, a conductor within said guide extending along a circle centered on the guide axis and in a plane perpendicular thereto, an electron discharge tube interposed in series in said conductor, and a signal indicating circuit comprising said tube.

7. In combination, a metal-sheathed dielectric guide, an electron discharge tube within. the guide at its receiving end, two terminal conductors extending oppositely from respective electrodes of the tube along the direction of lines of electric force of received waves in the guide, sensitive adjustment, the tube normally at a critical sensitive adjustment, and a signal indicating circuit comprising two electrodes 01' said tube.

8. In combination, a metal-sheathed dielectric guide, an electron discharge tube within the guide at its receiving end, two terminal conductors extending oppositely from respective elec-- trodes of the tube along the direction of lines of electric force of received waves in the guide, means to operate the tube normally with the discharge in a critical sensitive condition for reception, and a signal indicating circuit comprising two electrodes of said tube.

- 9. In combination, a metal-sheathed dielectric guide, a cold-cathode, two-electrode gas discharge tube within the guide at its receiving end,

two terminal conductors extending oppositely from respective electrodes of the tube along the direction of lines of electric force of received waves in the guide, means to operate the tube normally with the discharge in a critical sensitive state of ionization for reception, and a signal indicating circuit comprising the two electrodes of said tube.

10. In combination, a metal-sheathed dielectric guide, a high vacuum, three-electrode, electron discharge tube within the guide at its receiving end, two terminal conductors extending oppositely from respective electrodes of the tube along the direction of lines of electric force of received waves in the guide, and a signal indieagang circuit comprising two electrodes of said 11. In combination,

a cylindrical metalsheathed dielectric guide for symmetric electric waves, a hot-cathode electron discharge tube on its axis at the receiving end, said tube having a central electrode and a plurality of like electrodes around the central electrode, radial conductors from said like electrodes to the guide sheath, and a signal indicating circuit comprising said central electrode.

12. A dielectric guide comprising a metallic pipe, means for transmitting dielectrically guided waves therethrough, and means for receiving said waves comprising a space discharge device, said discharge device comprising one electrode centered on the axis of the guide and a plurality of other electrodes around said one electrode, and respective conductors extending outwardly from said other electrodes along the electric lines of force of said dielectrically guided waves.

13. In combination, a cylindrical metalsheathed dielectric guide, an electron discharge tube within the guide, and two opposite conductors therefrom extending through the sheath with mechanical sliding co'ntact so that the said tube can be adjusted across the guide.

14. In combination, a dielectric guide, two conductors in alignment within the guide, an interposed three-electrode vacuum tube having two of its electrodes connected to said conductors, conductors extending from said tube to the outside of the guide, an external oscillation generator system, an external signal indicating system, and a switch for the alternative connection of either of said systems to said last mentioned conductor.

15. A wave guide comprising a metallic pipe, means for propagating through said pipe electromagnetic waves of a character such that said guide exhibits a high-pass filter characteristic, and means for receiving said waves comprising a space discharge device within said pipe and means in the path of said wavesfor impressing said waves on said discharge device.

GEORGE C. SOU'I'HWORTH. ARCHIE P. KING. 

